Green is a color, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 520–570-nm. In the subtractive color system, it is not a primary color, but is created out of a mixture of yellow and blue, or yellow and cyan; it is considered one of the additive primary colors. On the HSV color wheel, the complement of green is magenta; that is, a purple color corresponding to an equal mixture of red and blue light. On a color wheel based on traditional color theory (RYB), the complementary color to green is considered to be red.

Green was symbolic of resurrection and immortality in Ancient Egypt; the god Osiris was depicted as green-skinned. Stories of the medieval period further portray it as representing love and the base, natural desires of man. Green is also known to have signified witchcraft, devilry and evil for its association with faeries and spirits of early English folklore. It also had an association with decay and toxicity. Actor Bela Lugosi wore green-hued makeup for the role of Dracula in the 1927-28 Broadway stage production. The color, when combined with gold, is seen as representing the fading away of youth. In the Celtic tradition, green was avoided in clothing for its superstitious association with misfortune and death. Green is thought to be an unlucky color in British and British-derived cultures, where green cars, wedding dresses, and theater costumes are all the objects of superstition. In high schools in the United States during the 1960s, it was widely believed that if someone wore green on Thursdays, it meant that they were homosexual.

In some Asian cultures the color green is often used as a symbol of sickness and/or nausea; however, in China, green is associated with the east, with sunrise, and with life and growth. Many Asian languages have no word distinguishing blue from green, though recently published dictionaries do make the distinction. (Thai: เขียว) besides meaning Green also means rank and smelly and other unpleasant associations. In Ancient China, green was the symbol of East and Wood, one of the main five colors. The Chinese term for “cuckold” sounds similar to the Chinese for “wearing a green hat”. It is because of this that it is extremely rare to see any Chinese man wearing a green hat.

Green is considered the traditional color of Islam, likewise because of its association with nature. This is for several reasons. First, Muhammad is reliably quoted in a hadith as saying that “water, greenery, and a beautiful face” were three universally good things.